The human tongue is an intricately configured muscular organ that plays a vital role during the physiological act of swallowing. During normal deglutition, the tongue first configures, then propels the ingested bolus from the oral cavity retrograde to the pharynx. From a clinical perspective, disorders of lingual function are exceedingly common in the elderly, in association with common neurological diseases, such as stroke, Parkinson's disease, and dementia, and are responsible for impaired nutrition and increased risk of aspiration pneumonia in these patient populations. Notwithstanding, there is minimal understanding of the way in which lingual muscular structure contributes to physiological function. The study of lingual mechanics has long been hampered by the complex myoarchitecture of the tissue and its material properties. As a result, mechanical function cannot be determined solely from global changes of shape, but necessitates the study of intramural dynamics. Our overall hypothesis is that the tongue functions as a muscular hydrostat, a unique structure in the human body, with the ability to both create motion and to provide the skeletal support for that motion. In order to test this hypothesis in the setting of human swallowing, we have considered the tongue from the perspective of a material continuum, and have thus depicted the tissue in terms of local fiber organization and strain. This project will study the quantitative relationship between three-dimensional myoarchitecture and regional mechanics during human swallowing. Our experimental approach uses non-invasive nuclear magnetic resonance imaging techniques to discern patterns of myoarchitecture and regional mechanics in vivo. In Specific Aim 1, the three-dimensional myoarchitecture of the tongue will be studied through the depiction of the local second order diffusion tensor derived from magnetic resonance imaging. In Specific Aim 2, the quantitative relationship between muscle fiber architecture and regional strain in association with swallowing will be determined by linkage of the structural measures with tagged magnetization. In Specific Aim 3, the regional mechanical adaptation to varying bolus volume and viscosity will be studied through combined diffusion tensor and tagged magnetization imaging under varying load conditions. This project should result in an improved understanding of structure-function relationships for the human tongue, and related human muscular hydrostats. It is anticipated that this understanding will result in novel hypotheses of pathological lingual function for patients with oropharyngeal dysphagia.